The present invention relates to an automated electronic instrument that will rapidly evaluate the alignment of both eyes objectively in primary, secondary and tertiary gaze, and the Bielschowsky head tilt positions and diagnose for phorias, tropias and intermittent tropias.
The present invention is referred to as a Trophorometer because it will measure tropias (manifest ocular misalignment) and phorias (latent deviation compensated for by the fusional reflex) to within one to two degrees. Computer image processing technology allows the measurement of the strabismus and obviates the use of prisms with their many shortcomings.
The present invention allows for screening for eye misalignment (eye muscle imbalance) by eye practitioners and to aid in the diagnosis of strabismus and to gauge treatment.
The eye alignment exam is an integral part of the routine eye examination performed by the eye specialist. Besides poor cosmesis, eye misalignment can be a cause for monocular visual loss (amblyopia), impaired binocular perception, reading difficulties, headaches, double vision, dizziness, nausea, and ocular toticollis (head tilt). Eye misalignment can also be a manifestation of a systemic disorder such as diabetic ocular neuropathy, thyroid eye disease, myasthenia gravis, child abuse/trauma, or a neurological disorder such as a cranial nerve palsy secondary to an intracranial lesion. In children, eye misalignment may be a presenting sign of a congenital cataract, or a life threatening eye tumor, a retinoblastoma. Proper diagnosis can enable the eye practitioner to initiate the appropriate surgical, optical, or medical treatment for the strabismus.
There are subjective and objective tests for measuring strabismus. Subjective methods involving patient response use dissimilar image or dissimilar target tests. Dissimilar image tests are based on the patient's response to diplopia produced by converting an isolated object of regard into different images of each retina (i.e. haploscope, Lancaster Red-Green Projectors). In these methods, the credibility of the results depends upon the skill of the examiner, the cooperation of the patient, and the existence of normal retinal correspondence without dense amblyopia or suppression.
The objective tests currently in use to evaluate eye alignment are based upon observing either the positions of the corneal light reflexes (Hirschberg and Krimsky Tests) or detecting eye refixation movements during occlusion and its removal (prism and cover test and the haploscope).
Other light reflexes such as the Purkinjie reflexes are used to track eye motions (Dual Purkinjie Eyetracker, SRL) and the red reflex to detect refractive differences between the eyes and gross misalignment. Other instruments make physical contact with the globe and measure eye movement but not eye position (EOG, ENG, Robinson Scleral Coil, force measuring forceps). The Nakayama photographic method measures small deviations with globe markers. A computer patient interaction system, the Computer Ocular Torsion Test, measures cyclotorsion deviation.
In the present invention, the Trophorometer will not only examine for small or large angle ocular deviations, but will also record pupil size, corneal diameters, lid fissure heights, interpupillary distance, and axial length. This ancillary information is of value to the eye practitioner for fitting contact lenses, sizing anterior chamber lenses, evaluating ptosis, fitting glasses, and planning eye muscle surgery for infantile esotropia.
The results of eye muscle balance testing performed as part of a routine eye examination generally depends on the skill of the examiner. It takes a trained observer to diagnose and measure tropias and phorias. Measurement of strabismus on the same patient can vary even between experienced examiners. There is no commercially available automated electronic instrument in ophthalmology to perform an eye alignment examination as there are computerized automated instruments to do visual fields, measure corneal curvatures, and do refractions.
Essentially, the present system consists of an electronic (CCD) camera set 33 cm in front of the patient that is level with, and midway between the eyes. Standard cover/uncover and alternate cover testing is done with the seated patient fixating on a small accommodative target in the center of the camera lens while secured in a special headrest. A sequence of images is captured and stored by an IBM compatible AT class computer. Change in position of each eye is compared in subsequent picture frames by the computer using an image processing algorithm that determines the direction and amplitude of the deviation and renders a diagnosis expressed in prism diopters and/or degrees.